Contractor: Department of Community and Environmental Medicine, UC Irvine

Contract Number: A5-129-33

As a result of a request by the California Air Resources Board for proposals dealing with fine particles, an innovative inhalation toxicology study, using a reliable animal model, was designed and successfully conducted. The objective of the study was to evaluate the respiratory system toxicity of both diesel-engine generated and propane-flame generated fine en particles, especially when an acid mixture of the type observed in California's air was also present. Atmospheres were generated into stainless steel exposure chambers and healthy rats breathed the pollutants nose-only for five hours per day for five consecutive days. The atmospheres studied included (a) dilute diesel exhaust soot + nitric acid + sulfuric acid and (b) propane-flame generated carbon soot + nitric acid + sulfuric acid. Groups of rats were also exposed to (a) the nitric and sulfuric acid mixture, (b) diesel soot, or (c) propane soot in order to examine the effects of the components of the soot + acids mixtures. Controls for exposure were rats exposed using the same schedule to purified air. When pollutants were present the concentrations of soot or of the combined acids were about 0.5 nq/rn3. The evaluation of potential health effects in exposed rats included: (a) measurement of respiratory tract clearance of insoluble tracer particles: (b) histopathologic examination of respiratory tract tissues, including autoradiographic measures of cell turnover (an index of cell killing): (c) morphometric analysis of deep lung tissues: and (d) measurement of effects on pulmonary alveolar macrophages (immunological endpoints). Biological effects were seen for each of the atmospheres studied. The propane soot + acids atmosphere produced a statistically significant (p < 0.1) delay in deep lung particle clearance: this effect was not seen with the diesel soot + acids atmosphere, however. Although none of the atmospheres produced lung cell killing, retained soot deposits were seen in the lung after exposure to atmospheres that contained soot. Diesel soot + acids, diesel soot alone and the acids alone all depressed pulmonary macrophage functions. Disturbances in deep lung structure were associated with the inhalation of diesel soot alone and when it was combined with acids. In summary, the agents studied were toxic in diverse ways. The effects of the combinations of soot plus acids appear to be attributable to the effects of the individual components. The interference with normal macrophage functions is likely to have the most significant implications to human health.